Make the test for IMS a bit more realistic.

src/tests/etag.vtc

@@ -136,7 +136,7 @@ varnish v1 -vcl+backend {
 
 	sub vcl_backend_response {
 		set beresp.http.foobar = beresp.http.content-encoding;
-		set beresp.filters = "br";
+		set beresp.filters = "unbr";
 	}
 }